In the production of bottles, tubes, vials and other tubular articles in multicavity blow molding machines from synthetic resin materials, a multicavity mold can be positioned beneath a row of extrusion heads so that respective parisons can be extruded downwardly into the open mold cavities. The mold cavities can be closed, i.e. by closing the multicavity blow mold, mandrels can be inserted into the parisons in the cavities and the parisons can be blown to the shape of the mold cavities. The parisons can be calibrated in tubular shaping portions of the mold cavity.
The closed blow mold can be displaced to the blowing and calibrating station in which the blowing mandrels are inserted into the parisons and, after blowing, the blow mold can be opened, the articles removed and the blow mold returned to alignment with the extrusion heads to receive new parisons.
Between the extrusion heads and the mold cavities, the dangling extruded parisons or tubes carry electrostatic charge.
Apparatus of this type is described, for example, in EP 0 570 393 B1 and the brochure entitled in English "Long Stroke Blow Molding Machines" published in January 1996 by Fischer W. Muller, Blasformtechnik, GmbH of Troisdorf, Germany.
In these blow molding machines the tubular extruded parisons may hang over a considerable distance between the extrusion head and the blow mold.
Because of the static charges developed on the parisons, the parisons tend to swing pendulum-fashion relative to the vertical and frequently cannot pass uniformly or reproducibly into the respective cavities. As a consequence, the wall thickness distribution in the mold cavity may be nonuniform and the product quality may diminish.
It has been proposed to solve this problem by providing an ionization device along side the extruded tubes or parisons and, for that purpose, a commercially available ionization bar has been provided at a high voltage of say 7 kV to ionize the atmosphere around the tubes or parisons utilizing a relatively low current of 0.25 mA. The bar carries a multiplicity of short electrodes in an insulating body, the electrodes projecting by about 2-4 mm from this body. An individual electrode may thus be turned toward each of the parisons and can develop a high voltage and generates positive and negative charge carriers which, in turn, are picked up by air molecules. In practice, however, this system has not been fully satisfactory since the desired charge dissipation often does not occur and efforts to enhance the charge dissipation by displacing the air forcibly brings about a one-sided cooling of the parisons which itself is detrimental and leads to defective products.